Rabbit beta-globin readthrough protein is the only naturally occurring readthrough protein in higher eukaryotes which does not involve a viral system. Since suppressor tRNAs have been used in gene therapy experiments and have been implicated in inhibiting viral expression, the readthrough protein has been isolated from rabbit reticulocytes in order to identify the amino acid at the suppression site and, therfore, to characterize the nonsense suppressor tRNA involved in the expression of this unique protein. Specific antibodies against this protein were prepared by synthesizing a 22 amino acid peptide which corresponds to the readthrough portion of the beta-globin readthrough protein, coupling the peptide to KLH protein and injecting the conjugated protein into a sheep. Specific antibodies were produced which were purified and used to isolate the readthrough protein for characterizing the amino acid at the suppression site.